It is already known that hard foam plastics which contain urethane groups can be produced by reacting compounds having a molecular weight of 400 to 10,000, and containing at least two hydrogen atoms which are reactive with isocyanates, with polyisocyanates in the presence of water and/or organic blowing agent and in the presence of flame-retarding agents which contain phosphorous, with the addition of activators, foam-stablilizers and optionally other foaming agents.
The use of phosphoric acid esters or phosphoric acids as flame-retarding agents for the production of foams which contain urethane groups is described in British patent specification Nos. 919,067 and 1,056,360. It has been found, however, that the use of these flame-retarding agents has numerous disadvantages.
Acids of phosphorus could not previously be used in foamable systems without serious disadvantages. There was either a risk of complete or partial collapse of the foam and excessive slowing down of the reaction or very pronounced faults, such as pits or cracks, appeared in the finished foam. In many formulations, it was also necessary to accept the incompatibility of the hydrophilic system in the hydrophobic system.
German Offlegungsschrift 2,129,198 describes a process for the production of foam plastics which uses addition compounds consisting of 0.1 to 15 mols of water and one mol of a lactam of the general formula: ##STR1## wherein X represents a CH-group, in which case R represents hydrogen and m an integer of from 0 to 9 or X represents a nitrogen atom, in which case R represents a C.sub.1 -C.sub.18 -alkyl or C.sub.7 -C.sub.15 -aralkyl group or a pyridine group optionally substituted by lower alkyl groups (C.sub.1 -C.sub.6) and m represents 3, in which addition compounds the water may be partly replaced by polyalcohols, polyamines or hydrazines.
The resulting foams do not have satisfactory flame-resistant characteristics.